ALFALFA GROWTH FOLLOWING RELEASE FROM DROUGHT STRESS

Compensatory growth (increased growth relative to normal) of alfalfa (Medicago sativa L.) when released from periods of drought stress has been observed or suggested. The objective of this research was to determine whether such compensatory growth does occur. Alfalfa was subjected to drought stress (plant water potential < -1.5 MPa) for 2 and 4 wk in a greenhouse study and 2, 4, and 6 wk in a field (Palouse silt loam soil, fine-silty, mixed, mesic Pachic Ultic Haploxerolls) study near Moscow, ID. Following harvest and removal of the drought stress, plant growth measurements were made after 30 d of growth in the greenhouse and biweekly during 5 wk of growth in the field. At the conclusion of the growth periods in both greenhouse and field studies, average stem length and dry matter yield of previously drought-stressed plants were 88 and 91%, respectively, compared with previously unstressed plants. Stem growth rates of field grown plants were less for the previously stressed plants only during the first 2 wk after release of stress. Stress treatments did not affect stems per plant (greenhouse) or stems per square meter (field). Leaf area per stem, however, for the previously drought-stressed plants was 122 and 108% compared with previously unstressed plants in the greenhouse and field, respectively. Leaf area was greater in the growth period following drought stress, but stem length and dry matter yield were reduced. Previous observations of apparent compensatory alfalfa growth after a drought may be attributed to increased leaf area.